150 



ROCHESTER ACADEMY OF SCIENCE. 



these hills they soon lowered themselves to the Iroquois level on the 

 east, merging with and becoming a part of that lake. More than 

 doubled in size by this annexation, Iroquois now became the suc- 

 cessor of Dawson in the Irondequoit region and continued its labors, 

 at a slightly lower level. 



Our map B (Plate V) of the early phase of Iroquois was 

 drafted under the former supposition that the Iroquois plane re- 

 mained practically stationary hereabouts during its long lifetime. 

 But it is now evident that this would necessitate the upward land 

 movement at the ]\Iohawk outlet being always exactly compensated 



LAKE IROQUOIS 



Fig. 5. Lake Iroquois Filling. Longitudinal profile of the lower Irondequoit 

 valley showing the great silt fillings during Lake Iroquois. The con- 

 vention used is not intended to accurately represent the real stratification. 

 Vertical exaggeration 17.5. Compare Map C (Plate VI) and Figures 

 4 to 8. 



for us by downcutting in the Little Falls gorge. It is more likely 

 that cataract recession at Little Falls would have terminated in a 

 rather sudden lowering of the lake surface. The Little Falls outlet, 

 moreover, carried prolonged and copious glacial drainage long prior 

 to Iroquois, and the latter has no high-level beaches in that region. 

 Therefore we must now believe that Iroquois entered our district at 

 a much lower level, after which its waters crept slowly back upon 

 us here as the land at Rome continued to rise. The recent discovery 

 of the Newfane beaches, already referred to, confirms this view. 

 It is far from certain, however, where (on a map) the first stand 

 of Iroquois was taken in our region since those first beaches are 

 buried deeply under silt. The map B is accordingly retained but 

 must be considered to depict only such a shore line as initial Iroquois 



